The observed trends (pre-lockdown, lockdown and eleven-year trend) of pH, EC, turbidity, TSS, DO, BOD, COD, TN, f. coli, t. coli, As and Pb at different locations throughout the stretch of the Santiago River are shown Fig. 2. The summary of the range, average value, measured variables in the river water samples between lockdown and pre-lockdown period, and the Mexican Standard Norm (2015) are provided in Table 1.
Table 1
Analytical data of water quality parameters during pre-lockdown and lockdown period at different locations of the Santiago River.
| | Pre- lockdown | Lockdown | Relative change (%) | Mexican permissible limits |
Stations | Parameters | Min | Max | Average | Min | Max | Average | Pre-lockdown vs lockdown | |
1 | pH | 7.1 | 9.4 | 7.738 | 6.6 | 9.1 | 7.762 | + 0.30 | 6.5–8.5 |
2 | Conductivity (uS/cm) | 408 | 1745 | 1187.308 | 852 | 1957 | 1220.077 | + 2.76 | - |
3 | DO (mg/L) | 0.08 | 8.95 | 3.778 | 0.02 | 6.98 | 3.368 | -10.84 | 5 |
4 | Turbidity (NTU) | 408 | 1873 | 1187.308 | 464 | 1957 | 1220.077 | + 2.76 | 3 |
5 | TSS (mg/L) | 7 | 370 | 38.385 | 7 | 245 | 35.769 | -6.81 | 50 |
6 | BOD (mg/L) | 2.03 | 425 | 46.208 | 2.09 | 183.61 | 39.866 | -13.72 | 30 |
7 | COD (mg/L) | 16.52 | 997.78 | 150.355 | 19.68 | 388.6 | 106.028 | -29.48 | 40 |
8 | f. coli (MPN/100 mL) | 90 | 110,000,000 | 12238289 | 40 | 46,000,000 | 8422265 | -31.18 | 1000 |
9 | t. coli (MPN/100 mL) | 230 | 110,000,000 | 12296617 | 70 | 46,000,000 | 10545466 | -14.24 | - |
10 | Total nitrogen (mg/L) | 0.96 | 69.74 | 17.095 | 0.42 | 52.95 | 18.211 | + 6.52 | - |
11 | As (mg/L) | 0.005 | 0.0148 | 0.008 | 0.0053 | 0.0146 | 0.010 | + 20.98 | 0.01 |
12 | Pb (mg/L) | 0.0072 | 0.0378 | 0.012 | 0.008 | 0.0141 | 0.010 | -19.76 | 0.01 |
3.1 Physiochemical characteristics
The range of pH was similar in pre-lockdown (7.1–9.4) and lockdown (6.6–9.1) (Table 1 and Fig. 2). Only a marginal increase of 0.30% and decrease of 1.16% was noted during lockdown in relation to pre-lockdown and eleven-year trend. Owing to the smaller variations between pre-lockdown and lockdown along the river course, data on pH serves much less in identifying possible pollution sources and do not generate essential information on water quality. As shown in Fig. 2, high levels of EC were observed in all stations of Santiago River, with an increase of 2.76% during lockdown period compared to pre-lockdown period (Table 1). Similarly, the EC values showed a slight escalation of 2.43% between lockdown and eleven-year trend (Table 2). The reasons can be found when analyzing the changes of EC levels registered among the stations. In the study area, we observed the increase of 3.76% in the metropolitan area (stations 4–7) indicating the augmentation of household wastes and waste disposal in the metropolitan area. More importantly, a decline of 5.56% in EC values was noted during lockdown in the sampling stations located at El Ahogado canal (11 and 12), which are greatly and usually affected by nearly 157 industrial wastewater discharges (Arellano-Aguilar et al. 2012; Ochoa and Bürkner, 2012; McCulligh and Vega Fregoso, 2019). This positive decline points out significant reduction in the industrial discharges of untreated wastewaters in proximate of El Ahogado canal as a consequence of lockdown measures.
Table 2
Relative change of water quality parameters in Santiago River (Mexico) between the lockdown and eleven-years data.
Stations | Parameters | 2009–2019 | 2020 | Change (%) |
1 | pH | 7.853 | 7.762 | -1.16 |
2 | Conductivity (uS/cm) | 1191.111 | 1220.077 | + 2.43 |
3 | DO (mg/L) | 3.114 | 3.368 | + 8.16 |
4 | Turbidity (NTU) | 1187.308 | 1220.077 | + 2.76 |
5 | TSS (mg/L) | 51.813 | 35.769 | -30.97 |
6 | BOD (mg/L) | 33.500 | 39.866 | + 19.00 |
7 | COD (mg/L) | 124.236 | 106.028 | -14.66 |
8 | f. coli (MPN/100 mL) | 2512287 | 8422265 | + 235.24 |
9 | t. coli (MPN/100 mL) | 3047798 | 10545466 | + 246.00 |
10 | TN (mg/L) | 19.745 | 18.211 | -7.77 |
11 | As (mg/L) | 0.007 | 0.010 | + 42.86 |
12 | Pb (mg/L) | 0.016 | 0.010 | -37.50 |
The BOD and COD values were considerably diminished during the lockdown in comparison to their respective pre-lockdown levels (Table 1). Their mean concentrations reduced by 13.72% and 29.48% in lockdown. More notably, the stations located at metropolitan area and El Ahogado canal displayed significant reductions (20% and 32%) of COD. Despite of the reduced levels of BOD and COD, nearly 30–76% of stations exceeded the permissible limits of Mexican Standard Norm (BOD = 30 mg/L; COD = 40 mg/L). In relation to eleven-year trend, BOD increased by 19% and COD decreased by 14.66% during lockdown. There has been an increment of 6.52% and decrement of 7.77% in TN values during lockdown in relation to pre-lockdown period and eleven-year trend (Tables 1 and 2). Generally, TN and BOD concentrations express the state of organic load, whereas COD levels reflect the trends of chemical contamination in a river system. As shown in Table 3, the significant correlations among BOD vs COD (r2 = 0.95) and TN (r2 = 0.88) indicates a common source of origin. In Santiago River, the organic and chemical loads mainly come from: (1) untreated gray water flow, (2) runoff from agricultural areas that carry excesses of nitrogen and phosphorous fertilizers and various agrochemicals (insecticides, fungicides, pesticides, etc.); and (3) industrial wastewater discharges, such as the stillage produced during the manufacture of beverages such as tequila and other industries that discharge organic waste into this river (McCulligh et al. 2007; Rizo-Decelis and Andreo, 2015; McCulligh and Vega Fregoso, 2019). From our results, it is highlighted that the diminished industrial activities during lockdown must have resulted in a notable level of reductions in BOD and COD, whereas agricultural activities that remained active might have contributed largely to increased TN levels.
Table 3
Correlation between water quality parameters during lockdown period in Santiago River (Jalisco), Mexico.
Parameters | pH | EC | DO | Turb | TSS | BOD | COD | f. coli | t. coli | TN | As | Pb |
pH | 1.00 | | | | | | | | | | | |
EC | - | 1.00 | | | | | | | | | | |
DO | 0.74*† | - | 1.00 | | | | | | | | | |
Turb | - | 1.00 | - | 1.00 | | | | | | | | |
TSS | - | - | - | - | 1.00 | | | | | | | |
BOD | - | 0.67* | -0.59* | 0.67* | 0.80*† | 1.00 | | | | | | |
COD | - | 0.61* | -0.59* | 0.61* | 0.82*†‡ | 0.95*†‡ | 1.00 | | | | | |
f. coli | - | - | - | - | - | - | 0.62* | 1.00 | | | | |
t. coli | - | 0.61* | - | 0.61* | - | 0.73*† | 0.78*† | 0.95*†‡ | 1.00 | | | |
TN | - | 0.80*† | - | 0.80*† | 0.73*† | 0.87*†‡ | 0.88*†‡ | 0.73*† | 0.85*†‡ | 1.00 | | |
As | - | - | - | - | - | - | - | - | - | - | 1.00 | |
Pb | - | - | - | - | 0.88*†‡ | 0.77*† | 0.83*†‡ | - | 0.61* | 0.85*†‡ | - | 1.00 |
p < 0.05*; 0.01†; 0.001‡ |
The DO concentrations remained below 5 mg/L that does not meet the permissible limits in majority of the stations for all the three assessment periods (pre-lockdown, lockdown and eleven-year trend) (Fig. 2). DO values decreased by 10.84% and increased by 8.16% in lockdown with respect to pre-lockdown and eleven-year trend (Tables 1 and 2). The low DO values suggest poor water quality and thereby, lack of oxygen in the water that have a negative impact on aquatic life. Maximum range (4% − 93%) of decreased DO levels were observed in the stations located at metropolitan area characterized with increased BOD levels. The correlation analysis demonstrated a negative relationship of DO with BOD (r2=-0.59) signifying that higher rate of bacterial decomposition of organic matter in the surface waters may have increased the demand of oxygen for their metabolic activities (Susilowati et al. 2018) and consequently, reduced the DO levels. Thus, the reductions in DO levels during lockdown in majority of the stations may be explained by the increment in BOD levels in those stations for the same period.
The values for turbidity in Santiago River for all the three assessment periods (pre-lockdown, lockdown and eleven-year trend) presented extremely higher orders of magnitude (> 300 times) with respect to permissible limits of 3 NTU set by Mexican Standard Norm (2015) (Fig. 2). The lockdown period displayed an increment of 2.76% in turbidity values compared to both pre-lockdown and eleven-year trend. The correlation analysis showed a strong association of turbidity with TN (r2 = 0.80) suggesting the slight increment in values linked to agricultural effluents. The TSS values on the other hand showed reductions of 6.81% and 30.97% in lockdown when compared to pre-lockdown and eleven-year trend (Fig. 2). The strong relationship of TSS with BOD (r2 = 0.80) and COD (r2 = 0.80) signifies that the decrease in TSS during lockdown period may be associated with lower BOD and COD values due to attenuated industrial activities.
3.2 Biological parameters
The trend of f. coli and t. coli counts in Santiago River water at the 13 sampling sites for three study periods is shown in Fig. 2. From our results, on one hand, the detection of f. coli throughout the stretch suggested the source of fecal contamination in the study area. It was previously reported that the entry of fecal matter is common and constant in the Santiago River (McCulligh et al. 2007; McCulligh and Vega Fregoso, 2019). Furthermore, untreated domestic sewages have been the main source of coliform bacteria, with other sources being direct discharge of waste from polluted irrigation water and storm runoff (Rodríguez-Tapia and Morales-Novelo, 2017; Seo et al. 2019). With the water of the Santiago River receiving constant fecal matter and exceeding Mexican Standard Norm (2015) permanently, it is an indicator for the presence of other disease-causing pathogenic bacteria and fungi that can impact human health coming into contact. Moreover, the intensive development of the metropolitan and industrial infrastructure could have added additional burden on the quality of river water. On the other hand, almost 90% of the stations reported higher concentrations of both f. coli and t. coli exceeding multiple folds of WHO (500 MPN/100 mL) and Mexican Standard Norm (1000 MPN/100 mL).
The monitored concentrations of f. coli in water samples ranged between 135 and 24200000 MPN/100 mL during lockdown period, whereas it was ranged from 160 to 78000000 MPN/100 mL in pre-lockdown period (Table 1). Whereas the t. coli counts were found between 150–25000000 MPN/100 mL and 230–55023000 MPN/100 mL during lockdown and pre-lockdown period. The results showed that t. coli counts reduced by approximately 14.24% from 12296617 to 10545466 MPN/100 mL in 50% of sampled stations between the lockdown and pre-lockdown period. Similarly, the contents of f. coli declined sharply by 31.18% from 12238289 to 8422265 MPN/100 mL in 7 out of 13 stations during the lockdown and pre-lockdown period. In particular, a significant reduction of 20% of coliform bacteria (f. coli and t. coli) was recorded in the stations located at El Ahogado canal. These observations clearly indicate the reduced inflow of industrial effluents during lockdown and further confirmed by the strong positive associations of coliform bacteria with industrial organic pollutants like BOD (r2= - ; 0.73) and COD (r2 = 0.62; 0.78). However, variations in the relative change of coliform bacteria were opposite when compared to eleven-year trend. Both coliforms augmented four times during lockdown compared to eleven-year trend (Table 2). This makes clear that although the coliform bacteria concentration fluctuated between lockdown and pre-lockdown period, it was generally in an upward trend over the decade. As seen in Table 3, the observed no associations of pH and DO with coliforms in the Santiago River which appeared to be a natural process due to the coliform bacteria proliferation and the occurrence of carbon dioxide (Seo et al. 2019). Nonetheless, the high concentrations of coliform pointed out the potential health threats from water-borne diseases and the immediate need for coliform management in the study area.
3.3 Metals
The concentrations of As and Pb showed significant variations in the lockdown period with respect to pre-lockdown and eleven-year trend (Fig. 2; Tables 1 and 2). When we look at the As levels, it increased from 0.008 mg/L in pre-lockdown to 0.010 mg/L during lockdown accounting for 20.98% increment. Likewise, the As levels increased 42% in lockdown period compared to eleven-year trend. In lockdown period, As presented no correlations with other water quality parameters suggesting its unique source origin in the Santiago River. The elevated concentrations of As have been previously attributed in Santiago river to industrial wastewater discharges (Arellano-Aguilar et al. 2012; Ochoa and Bürkner, 2012; McCulligh and Vega Fregoso, 2019) and even with decreased industrial activities during COVID-19 outbreak, the As levels were higher in this study. The reason may be the low levels of suspended particles during lockdown period that would aid in retention of As in sediments from the above water column through binding or (co)precipitation (Smedley and Kinniburgh, 2002; Rubinos et al. 2003; Barral-Fraga et al. 2020). Similarly, an increased trend of As (42.86%) with decreased TSS (30.97%) was observed between lockdown and eleven-year trend. On contrary, a maximum decrease of 24.52% was noticed in the case of Pb during lockdown. The sampling stations (11 and 12) located in El Ahogado canal receiving industrial wastewaters from Guadalajara metropolitan area presented higher levels of Pb with 0.21 mg/L and 0.19 mg/L during pre-lockdown and drastically reduced to 0.014 mg/L and 0.013 mg/L in lockdown, reflecting the influence of restricted industrial activities. More supportively, Pb was positively correlated with industrial pollutants like BOD (r2 = 0.77) and COD (r2 = 0.83) (Table 3). In addition, 8 out of 13 stations registered sharp reductions ranging from 5–70% in Pb levels. Likewise, the eleven-year trend when compared with lockdown period revealed 13.78% reductions in Pb. Furthermore, according to Mexican Standard Norm (2015), the maximum allowable limit for As and Pb is 0.01 (mg/L). In pre-lockdown, 3 stations displayed As levels above the permissible limits, whereas 6 stations exceeded the limits during lockdown (Fig. 2). The exceedances of Pb levels were recorded in 9 and 4 stations during pre-lockdown and lockdown period, respectively. Appraisingly, stations 2–4 showed higher values (0.012 to 0.020 mg/L) than permissible levels in pre-lockdown and fell under the limits (0.006 to 0.01 mg/L) during lockdown.
3.4 Factor analysis
Factor analysis (FA) was performed on the normalized dataset (12 parameters) analyzed for both pre-lockdown and lockdown period, to understand their compositional pattern, interrelationship between the parameters and identify the factors influencing each one. Three factors contributed for 91.74% and 84.71% of the total variance in the dataset of pre-lockdown and lockdown periods. The factor analysis loadings for the study period are presented in Fig. 3a-b. In case of pre-lockdown (Fig. 3a), Factor 1 exhibited strong positive loadings of TSS, BOD, COD, f. coli and t. coli. This factor may be termed as “organic pollution factor” and explained as representing influences from point sources such as industrial effluents and domestic wastewater. The El Ahogado canal (stations 11 and 12) and in the downstream section, Verde River (station 7) and Zula River (station 13) are the main hotspots where the major events of urban and industrial wastewater discharges from NE Guadalajara city and nearby regions occur. Factor 2 had negative loadings on pH, DO and As. This factor may be termed as “metal pollution factor” and indicates that pH and DO seemed to favor the enrichment of As in dissolved phase. Finally, EC, turbidity and TN were found in Factor 3 and termed as “inorganic pollution factor” demonstrating their inflow mainly from agricultural and municipal effluents.
When compared to pre-lockdown, the lockdown period showed significant variations in the factor loadings (Fig. 3b). Factor 1 had strong positive loadings of TSS, BOD, COD, TN and Pb. This factor can be termed as “mixed pollution factor” and explained as one typical type of mixed pollution consisting of point sources like industrial wastewater and non-point sources associated with agricultural activities. Factor 2 showed negative loadings for pH and DO. Unlike in pre-lockdown, Factor 3 termed as “pathogenic pollution factor” presented strong positive loadings for f. coli and t. coli and no associations with other organic pollutants like BOD and COD, clearly reflecting their sources from non-point pollutants like fertilizers, livestock feces, sewage discharges rather than industrial wastewaters. Overall, in FA analysis, the differences observed between pre-lockdown and lockdown evidently demonstrated the positive effects of diminished anthropogenic activities on the water quality parameters. Furthermore, it revealed three main contamination sources in Santiago River as: (1) wastewaters associated to industrial activities; (2) urban wastewaters and sewage discharges; and (3) agricultural effluents.
3.5 Water quality Index (WQI)
WQI estimation allows to determine the influence of individual water quality parameter on the overall water quality and its suitability for drinking purpose. In this study, WQI was calculated by considering WHO (2011) and Mexican Standard Norm (2015). The WQI values of the water samples from all the 13 sampling sites for each assessment period are summarized in Table 4. Regardless of the assessment period, the WQI values for water samples from 13 sampling sites ranged from 82.29 to 345.63 and over 97% of the samples are above 100. The highest WQI value of 230.37, 345.63 and 221.78 was recorded in eleven-year trend, pre-lockdown and lockdown, whereas lowest WQI value was 103.18, 93.71 and 82.29, respectively. Moreover, we observed that the WQI value showed a mixed pattern of change in the water samples of stations between assessment periods (Table 4). For instance, the comparison of WQI values between pre-lockdown and lockdown periods showed improvements in 8 out of 13 stations ranging from 0.78–45%, with an overall change of 4.5% in the Santiago River indicating positive effect of reduced industrial and commercial activity. Similarly, when WQI values of eleven-year trend were compared, the lockdown period displayed enhancement between 6.2% and 26.50% in river waters of majority of stations (11 out of 13), with an overall change of 6% suggesting short-term improvements of surface water quality along the river. Especially, the sampling stations located in the metropolitan area showed an improvement of 0.65% and 12.62% in the lockdown period than pre-lockdown and eleven-year data. The minimal effluent discharge with the temporary shutdown of industrial and commercial activities during the lockdown has likely reduced the level of contamination in the study area. Thus, the assessment of WQI data demonstrates that the river water quality has comparatively been improved in years. Nevertheless, the results also revealed that majority of the river water samples fall under unsuitable water category (WQI > 100), indicating water quality of nearly 90% of the whole region is greatly deteriorated due to industrialization and various human activities like the inflow of direct sewerage from residential and commercial establishments, lack of proper sanitation system, agricultural run-off, direct disposal of untreated effluents from small scale industries and factories and unabated dumping of solid wastes by the communities residing alongside the river, etc. Although the WQI analysis results unveiled considerable improvements during lockdown period comparably to pre-lockdown and eleven-year trend, the fact about abrupt deterioration and the persistence of pollution for decades in Santiago River cannot be ignored and requires special attention from government authorities.
Table 4
Summary of WQI values of water samples from 13 sampling sites for each assessment period.
Stations | 2009–2019 | Classification | 2019 | Classification | 2020 | Classification |
1 | 164.85 | ***** | 105.18 | ***** | 126.33 | ***** |
2 | 108.69 | ***** | 94.55 | **** | 82.29 | **** |
3 | 114.80 | ***** | 93.71 | **** | 84.37 | **** |
4 | 124.31 | ***** | 114.13 | ***** | 118.34 | ***** |
5 | 136.71 | ***** | 121.44 | ***** | 100.84 | ***** |
6 | 147.44 | ***** | 144.23 | ***** | 143.12 | ***** |
7 | 184.17 | ***** | 159.82 | ***** | 194.96 | ***** |
8 | 176.24 | ***** | 141.61 | ***** | 138.93 | ***** |
9 | 103.18 | ***** | 100.06 | ***** | 116.57 | ***** |
10 | 134.35 | ***** | 178.17 | ***** | 173.96 | ***** |
11 | 230.37 | ***** | 345.63 | ***** | 190.20 | ***** |
12 | 164.14 | ***** | 186.43 | ***** | 221.78 | ***** |
13 | 149.45 | ***** | 97.89 | **** | 126.77 | ***** |
Overall Santiago River | 149.13 | ***** | 144.84 | ***** | 139.88 | ***** |
***** = unsuitable for drinking; **** = very poor. |